commit-check
@@ -46,8 +46,8 @@ Overview
 **Commit Check** is a lightweight policy engine for Git commit metadata.
 
 It validates commit messages, branch names, author identity, signoff trailers,
-and push safety — using one versioned TOML policy across local hooks, CI,
-GitHub Actions, and AI automation.
+AI attribution policy, and push safety — using one versioned TOML policy across
+local hooks, CI, GitHub Actions, and AI automation.
 
 - **One policy file:** ``cchk.toml``
 - **Multiple enforcement points:** CLI, pre-commit, CI / GitHub Actions
@@ -139,6 +139,9 @@ To customize the behavior, create a configuration file named ``cchk.toml`` or ``
     require_signed_off_by = false
     # Bypass checks for bot/automation authors and co-authors:
     ignore_authors = ["dependabot[bot]", "renovate[bot]", "copilot[bot]"]
+    # AI attribution policy: "ignore" (default) or "forbid"
+    # "forbid" rejects commits with known AI tool signatures
+    ai_attribution = "forbid"
 
     [branch]
     # https://conventionalbranch.org

@@ -72,5 +72,8 @@
     "require_signed_off_by": False,
 }
 
+# AI attribution defaults
+DEFAULT_AI_ATTRIBUTION = "ignore"  # "ignore" | "forbid"
+
 
 __version__ = version("commit-check")
@@ -0,0 +1,76 @@
+"""AI tool signature detection logic.
+
+This module provides the public API for detecting AI tool signatures in commit
+messages.  The signature data (tool definitions and patterns) lives in
+:mod:`commit_check.ai_signatures_data`.
+
+Typical usage::
+
+    from commit_check.ai_signatures import detect_ai_signatures
+
+    result = detect_ai_signatures(
+        "feat: init\\n\\nCo-authored-by: Claude <noreply@anthropic.com>"
+    )
+"""
+
+from __future__ import annotations
+
+import re
+
+from commit_check.ai_signatures_data import ALL_KNOWN_TOOLS as _ALL_KNOWN_TOOLS
+
+# Re-export for convenience — consumers can import everything from
+# commit_check.ai_signatures without knowing about the data/logic split.
+ALL_KNOWN_TOOLS = _ALL_KNOWN_TOOLS
+
+
+#: Flat list of all compiled patterns for bulk scanning.
+#: Each tuple is ``(regex, tool_name, description, kind)``.
+ALL_PATTERNS: list[tuple[re.Pattern[str], str, str, str]] = [
+    (p.regex, tool.name, p.description, p.kind)
+    for tool in ALL_KNOWN_TOOLS
+    for p in tool.patterns
+]
+
+
+def detect_ai_signatures(message: str) -> list[dict[str, str]]:
+    """Scan *message* for known AI tool signatures.
+
+    :param message: The full commit message (subject + body) to scan.
+    :returns: A list of dicts, one per matched signature, each with keys
+        ``"tool"``, ``"kind"``, ``"description"``, and ``"matched_text"``.
+        Returns an empty list when no signatures are found.
+
+    Example::
+
+        >>> detect_ai_signatures(
+        ...     "feat: init\\n\\nCo-authored-by: Claude <noreply@anthropic.com>"
+        ... )
+        [{'tool': 'Claude Code', 'kind': 'trailer', ...}]
+    """
+    results: list[dict[str, str]] = []
+    seen: set[str] = set()
+
+    for regex, tool_name, desc, kind in ALL_PATTERNS:
+        for match in regex.finditer(message):
+            matched = match.group(0).strip()
+            if matched not in seen:
+                seen.add(matched)
+                results.append(
+                    {
+                        "tool": tool_name,
+                        "kind": kind,
+                        "description": desc,
+                        "matched_text": matched,
+                    }
+                )
+
+    return results
+
+
+def has_ai_signature(message: str) -> bool:
+    """Return ``True`` if *message* contains any known AI signature."""
+    for regex, _tool_name, _desc, _kind in ALL_PATTERNS:
+        if regex.search(message):
+            return True
+    return False
@@ -0,0 +1,257 @@
+"""Known AI tool signatures — pure data, no detection logic.
+
+This module defines the data structures and the curated registry of known AI
+coding tool signatures.  To add a new tool, define a ``KnownAiTool`` entry
+with its patterns and add it to ``ALL_KNOWN_TOOLS``.
+
+The detection logic lives in :mod:`commit_check.ai_signatures`.
+"""
+
+from __future__ import annotations
+
+import re
+from dataclasses import dataclass, field
+
+
+@dataclass(frozen=True)
+class AiSignaturePattern:
+    """A single pattern that identifies AI tool usage in a commit message.
+
+    :param regex: A compiled regex that, if matched anywhere in the commit
+        message body, indicates the corresponding tool was involved.
+    :param kind: ``"trailer"`` for structured ``Key: value`` footer lines
+        (matched case-insensitively), ``"body_marker"`` for any other text
+        marker.
+    :param description: Human-readable description of what is matched.
+    """
+
+    regex: re.Pattern[str]
+    kind: str  # "trailer" | "body_marker"
+    description: str = ""
+
+
+@dataclass(frozen=True)
+class KnownAiTool:
+    """A known AI coding tool and its commit-message signatures.
+
+    :param name: Short display name (e.g. ``"Claude Code"``, ``"GitHub Copilot"``).
+    :param patterns: One or more signature patterns that indicate this tool.
+    """
+
+    name: str
+    patterns: list[AiSignaturePattern] = field(default_factory=list)
+
+
+# ---------------------------------------------------------------------------
+#  Pattern helpers
+# ---------------------------------------------------------------------------
+
+
+def _trailer(
+    key: str, value_pattern: str = r".*", description: str = ""
+) -> AiSignaturePattern:
+    """Build a trailer pattern for a structured ``Key: value`` line.
+
+    The match is case-insensitive and anchors the key at the start of a line.
+    """
+    raw = rf"^{re.escape(key)}:\s*{value_pattern}\s*$"
+    return AiSignaturePattern(
+        regex=re.compile(raw, re.IGNORECASE | re.MULTILINE),
+        kind="trailer",
+        description=description or f"``{key}:`` trailer",
+    )
+
+
+def _body_marker(pattern: str, description: str = "") -> AiSignaturePattern:
+    """Build a free-text body marker pattern."""
+    return AiSignaturePattern(
+        regex=re.compile(pattern, re.MULTILINE),
+        kind="body_marker",
+        description=description,
+    )
+
+
+# ---------------------------------------------------------------------------
+#  Known tool signatures
+# ---------------------------------------------------------------------------
+
+# --- Anthropic Claude Code / Claude CLI ---
+CLAUDE_CODE = KnownAiTool(
+    name="Claude Code",
+    patterns=[
+        # Standard Co-authored-by trailer added by Claude Code.
+        # When an email is present, anchor to known AI noreply addresses
+        # to avoid false positives with human co-authors named Claude.
+        _trailer(
+            "Co-authored-by",
+            r"Claude(?: Code)?"
+            r"(?:\s*<(?:noreply@anthropic\.com"
+            r"|\d+\+Claude@users\.noreply\.github\.com)>)?",
+            "``Co-authored-by: Claude`` trailer",
+        ),
+        # Assisted-by trailer (Linux kernel style, with optional tool list)
+        _trailer(
+            "Assisted-by",
+            r"Claude:\S+(?:\s+\S+)*",
+            "``Assisted-by: Claude:<model> [tools]`` trailer",
+        ),
+        # Body marker: generated-with notice
+        _body_marker(
+            r"🤖\s*Generated\s+(?:with|by)\s+\[?Claude",
+            "``🤖 Generated with Claude`` body marker",
+        ),
+        # Session ID trailer (Claude Code sometimes adds this)
+        _trailer("Claude-Session", r"\S+", "``Claude-Session:`` trailer"),
+        # Workflow ID trailer
+        _trailer("Claude-Workflow", r"\S+", "``Claude-Workflow:`` trailer"),
+    ],
+)
+
+# --- GitHub Copilot ---
+COPILOT = KnownAiTool(
+    name="GitHub Copilot",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Copilot"
+            r"(?:\s*<\d+\+Copilot@users\.noreply\.github\.com>)?",
+            "``Co-authored-by: Copilot`` trailer",
+        ),
+    ],
+)
+
+# --- OpenAI Codex ---
+CODEX = KnownAiTool(
+    name="OpenAI Codex",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Codex\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Codex`` trailer",
+        ),
+    ],
+)
+
+# --- Gemini (Google) ---
+GEMINI = KnownAiTool(
+    name="Gemini",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Gemini\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Gemini`` trailer",
+        ),
+    ],
+)
+
+# --- Cursor ---
+CURSOR = KnownAiTool(
+    name="Cursor",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Cursor\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Cursor`` trailer",
+        ),
+    ],
+)
+
+# --- Devin ---
+DEVIN = KnownAiTool(
+    name="Devin",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Devin\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Devin`` trailer",
+        ),
+    ],
+)
+
+# --- Aider ---
+AIDER = KnownAiTool(
+    name="Aider",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Aider\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Aider`` trailer",
+        ),
+        # aider appends "(aider)" to the author name
+        _trailer(
+            "Co-authored-by",
+            r"[^<]+\(aider\)\s*(?:<[^>]*>)?",
+            "``Co-authored-by: ... (aider)`` trailer",
+        ),
+    ],
+)
+
+# --- Windsurf (Codeium) ---
+WINDSURF = KnownAiTool(
+    name="Windsurf",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Windsurf\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Windsurf`` trailer",
+        ),
+    ],
+)
+
+# --- Tabby ---
+TABBY = KnownAiTool(
+    name="Tabby",
+    patterns=[
+        _trailer(
+            "Co-authored-by",
+            r"Tabby\s*(?:<[^>]*>)?",
+            "``Co-authored-by: Tabby`` trailer",
+        ),
+    ],
+)
+
+# --- Generic / catch-all AI patterns ---
+GENERIC_AI = KnownAiTool(
+    name="Generic AI",
+    patterns=[
+        # Catch AI agent model identifiers in Co-authored-by
+        # (e.g. claude-sonnet-4, gpt-4-turbo, gemini-1.5-pro).
+        # A hyphenated model suffix is required so bare human first names
+        # ("Claude", "Gemini") are NOT flagged, regardless of the email.
+        _trailer(
+            "Co-authored-by",
+            r"(?:claude|gpt|gemini)[\w.]*-[\w.-]+(?:\s*<[^>]*>)?",
+            "``Co-authored-by`` with AI model name",
+        ),
+        # Catch Assisted-by trailer (Linux kernel style) regardless of agent,
+        # with optional trailing tool list.
+        _trailer(
+            "Assisted-by",
+            r"\S+:\S+(?:\s+\S+)*",
+            "``Assisted-by: <tool>:<model> [tools]`` trailer (kernel style)",
+        ),
+        # Catch common body markers
+        _body_marker(
+            r"^Generated\s+(?:by|with)\s+(?:AI|artificial intelligence)",
+            "``Generated by AI`` body marker",
+        ),
+    ],
+)
+
+# ---------------------------------------------------------------------------
+#  Master registry — ordered by specificity (most specific first)
+# ---------------------------------------------------------------------------
+
+#: All known AI tools, ordered so that more specific patterns are checked first.
+ALL_KNOWN_TOOLS: list[KnownAiTool] = [
+    CLAUDE_CODE,
+    COPILOT,
+    CODEX,
+    GEMINI,
+    CURSOR,
+    DEVIN,
+    AIDER,
+    WINDSURF,
+    TABBY,
+    GENERIC_AI,
+]
@@ -132,6 +132,7 @@ def validate_message(
         "allow_empty_commits",
         "allow_fixup_commits",
         "allow_wip_commits",
+        "ai_attribution",
     ]
     return _run_checks(check_names, context, cfg)